1. Field of the Invention
The present invention relates to a reduction gear unit for use in various kinds of motive or or actuating mechanisms or systems.
2. Description of the Prior Art
As well known, a variety of motive or actuating mechanisms or systems for executing an intended mechanical motion are by and large equipped with a reduction gear mechanism in order to reduce the rate of a drive force generated from a drive source to thereby transform the drive force into a greater one.
Generally, the reduction gear mechanism comprises multiple combinations of plural different gears, and there as been an increased demand, in view of small-size and weight-light oriented tendency, for a simplified structure of reduction gear mechanisms with a highest possible ratio of reduction.
In the past, one of the prior attempts to attain this simplified reduction gear mechanism has been known from the Japanese Patent Publication No. 49-48691, for instance.
According to this conventional mechanism, as shown in FIG. 1, there is provided a combination of an internally toothed annular plate member (1) and externally toothed disc member (2), wherein the number of the teeth of the latter is reduced by one as compared with that of the former. Hence, it is observed that the externally toothed disc member (20) is partially meshed with the internally toothed annular plate member (1). The externally toothed disc member (2) is fixed stationary whereas the internally toothed annular plate member (1) is supported in an eccentrically rotatable manner by the eccentric rotation member (3) which comprises a rotation shaft (3a) and an eccentric ring (3b), the rotation shaft (3a) being at its one end fixed to the drive shaft of a motor (not shown), passing rotatably through the center of the externally toothed disc member (2), and being fixed at its other end fixed to the eccentric ring (3b). When the motor is energized to rotate the eccentric rotation member (3), the internally toothed annular member (1) is eccentrically rotated relative to the shaft (3a) and thus rolled around the externally toothed disc member (2) in a partially-meshed and slightly-angled relationship at the ratio of tooth number between the two toothed members (1)(2) which is obtained from the difference therebetween of the tooth numbers of one, as stated above. Thus, the rotation speed of the motor is reduced through the internally toothed annular plate member (1), and imparted as a reduced rotation output to other motive mechanism.
However, the above-constructed reduction gear mechanism has a limitation attendent therein in its adaptability for use with other relative motive mechanisms in that the internally toothed annular plate member (1) is formed in a plate-like shape, not as a shaft, and the eccentric arrangement of such plate member (1) simply imparts an eccentrical rotation as it is to other relative mechanimsms, which makes the connection difficult between this reduction gear mechanism with the gear mechanisms of other relative mechanical systems or requires a special connecting means therebetween.
Moreover, another drawback found in this prior art is that a large ratio of its input and output is not attainable because of a limit in creating a smallest possible pitches of the teeth of the two toothed members (1)(2) in view of their structural strength limits, although certainly creating the smallest pitches of the teeth of those members (1)(2) leads to a far greater ratio of input and output for a desired large reduction of drive rate.